Effect of water-soaking duration on the low-temperature performance of steel slag asphalt mixtures characterized by acoustic emission technology

Steel slag undergoes hydration-induced expansion after water exposure, causing internal damage and reducing low-temperature fracture resistance. To clarify the mechanisms by which water soaking affects the low-temperature performance of steel slag asphalt mixtures (SSAM) at different temperatures, semi-circular bending (SCB) tests and acoustic emission (AE) monitoring were conducted. The failure process was characterized under different water-soaking durations (0–6 d) and test temperatures of 0 °C and −20 °C. The results showed that the failure process of steel slag asphalt mixtures could be divided into four stages, namely compaction, elastic deformation, plastic failure, and accelerated failure. Water soaking accelerated the damage evolution of SSAM at 0 °C by shortening the elastic deformation and plastic failure stages. At −20 °C, the disappearance of the plastic failure stage resulted in a transition toward brittle failure. Type A signals represented high-energy AE events above the statistical boundary, whereas Type B signals were below it. At 0 °C, the proportion of Type A signals increased from 5.0% in the unsoaked specimens to 35.9% after 4 d of water soaking and then decreased to 28.4% after 6 d, while Type B signals dominated at −20 °C (>89.6%) for all soaking durations. Water soaking enhanced energy-release heterogeneity at 0 °C and promoted tensile-dominated failure at −20 °C. A negative linear trend was observed between fracture energy and cumulative energy at low temperature, while the Weibull-based model captured the transition from stable damage accumulation to rapid failure. The results provide an understanding of the damage evolution of SSAM after water soaking and guide the design of steel slag asphalt mixtures with improved low-temperature cracking resistance.